Servo motors for vehicle brake systems

ABSTRACT

The invention relates to servo motors for vehicle brake systems, and particularly relates to servo motors of the type having two contiguous fluid-tight compartments separated by a diaphragm supported on a deflecting plate comprising a plurality of circumferentially spaced fingers, and controlled by a pair of concentrically disposed valve seats. A deflecting plate for such a servo motor is disclosed, which comprises a plurality of spaced rigid fingers held in regular circularly spaced relationship of which some, but not all, are adapted to pivot alternatively about the concentric valve seats. By this means excessive hysteresis effects associated with this type of servo motor may be reduced.

[ 51 Sept. 4, 1973 SERVO MOTORS FOR VEHICLE BRAKE SYSTEMSYardley.....r....................... Robinette................... ..m91/369 8 John James Camm, Victoria, Australia Melbourne.

[75] Inventor:

Primary ExaminerPaul E. Maslousky Att0rne v Scrivener, Parker. Scrivener& Clarke ABSTRACT [73] Assignee: Girling Limited, Birmingham.

England The invention relates to servo motors for vehicle brake systems,and particularly relates to servo motors of the type having twocontiguous fluid-tight compartments separated by a diaphragm supportedon a deflecting plate comprising a plurality of circumferentially spacedfingers, and controlled by a pair of concentrically disposed valveseats. A deflecting plate for such a servo motor is disclosed, whichcomprises a plurality of spaced rigid fingers held in regular circularlyspaced relationship of which some, but not all, are adapted to pivotalternatively about the concentric valve seats. By this means excessivehysteresis effects associated with this type of servo motor may bereduced.

a 3 n N B nm W2 n n mm 1 .m mm 4 w 6 e m m l 4 F l .l U u y a G H ll 2 pn h H 6 A n C. J1 O u M 7 W 0 .W W "HS L m ca d F M m P N mmk F A JUIIF 1. l ill. 2 l 0 2 8 2 2 3 555 9 Claims, 2 Drawing Figures [56]References Cited UNITED STATES PATENTS u d n a R 3,183,789 5/1965Stelzer..... 3,246,578 4/1966 Patented Sept. 4, 1973 3,756,124

2 Sheets-Sheet 1 IO --F 7 cs. 2.--

4o 44 46 28 3s 56 so 46 SERVO MOTORS FOR VEHICLE. BRAKE SYSTEMS Thisinvention concerns servo motors for vehicle brake systems and relatesmore generally to a fluid flow control valve assembly for use especiallyin such servo motors.

In our British Patent No. 1,144,567 there is described a servo motor fora vehicle brake system of the kind which includes a pair of fluidpressure sources of different fluidpressures and which comprises aninternally hollow housing, a movable wall within said housing anddividing the hollow interior thereof into contiguous first and secondfluid chambers, a motor output member displaceable by said wall andextending externally of said housing, and fluid flow control valvemeans. for selectively connecting the first chamber to said fluidpressure sourceswith the second chamber permanently connected to one ofsaid sources only, thereby enabling a fluid pressure differential to beestablished between said chambers for moving said wall within saidhousing, said control valve means comprising a valve seat member formedwith a pair of spaced passage means, a pair of relatively stationaryconcentric valve seats on said member and each circumscribing one ofsaid passage means, and a common valve closure memberengageable with andselectively tiltable about each seat to thereby open the passage meanscircumscribed by the other said seat, the end of one of said passagemeans remote from said valve seats being permanently connected to one ofsaid fluid sources and the corresponding end of the other said passagemeans being permanently connected to said first chamber, and saidmovable wall comprising an annular elastic diaphragm whose outerperiphery is rigidly fixed relative to the housing and a deflectingplate for operating the common valve closure member.

In that patent, the deflecting plate comprises a plurality of equallysized, radially extending fingers which are held in circularly spacedrelationship and which are all selectively pivotable about each saidvalve seat to thereby achieve said tilting of the common valve closuremember according to whether air is being admitted into one of thechambers to actuate the booster or air being withdrawn from said chamberto relieve the brakes. Because the valves are concentric, the pivot armis shorter when the levers formed by said fingers pivot about the outervalve seat to open the atmosphere connecting than when they pivot aboutthe inner valve seat to open the vacuum connection. As is explainedfurther below, this gives rise to a hysteresis" effect which results inthe reaction force experienced by an operator on applying the brakesbeing greater than the reaction force experienced on releasing thebrakes.

The present invention seeks to maintain a difi'erential forcerequirement between the two alternative pivoting conditions, whilstensuring that it does not exceed an acceptable amount.

According to one aspect of the present invention, the deflecting platecomprises a plurality of first, radially extending, rigid fingers heldin circularly spaced relationship which are selectively pivotable abouteach said valve seat to thereby achieve said tilting of the common valveclosure member and a plurality of second, radially extending, rigidfingers which are shorter than said first fingers and whose radiallyinner ends are located outwardly of the radially outer of saidconcentric valve seats.

According to a second aspect of the invention, there is provided a fluidflow control valve assembly which comprises a valve seat member formedwith a pair of radially spaced passage means, a pair of relativelystationary and substantially concentric valve seats on said member, saidvalve seats each circumscribing one of said passage means, a commonvalve closure member engageable with and selectively pivotable abouteach seat to thereby open the passage means circumscribed by the othersaid seat, and deflecting meansfor operating the valve closure member,said deflecting means comprising a plurality of first, radiallyextending, rigid fingers held in circularly spaced relationship whichare selectively pivotable about each said valve seat to thereby achievesaid pivoting of the common valve closure member and a plurality ofsecond, radially extending, rigid fingers which are shorter than saidfirst fingers and whose radially inner ends are located outwardly of theradially outer of said concentric valve seats.

The invention will be described further, by way ofexample, withreference to the accompanying drawings, in which:

FIG. 1 is an axial cross section of part of a servo booster embodyingthe invention; and

FIG. 2 is a section taken along the line A-A in FIG. 1.

The deflecting plate of the invention constitutes an improvement whenused in the servo motor described in our British Patent specificationNo. I 144567, the entire disclosure of which is incorporated herein byway of reference. The accompanying drawings both show part of a servobooster modified according to the invention, the remainder of the servobooster being as illustrated and described in our above mentionedBritish specification No. 11445677 Referring now to the drawings, abrake booster generally designated 10 comprises a diaphragm l2 fixed toa valve seat member 14 by means of an annular garter retainer 16. Adeflecting plate 18 (more clearly shown in FIG. 2) is located adjacentto, and supports the diaphragm 12. The deflecting plate 18 comprisesthree rigid fingers 20 circumferentially and uniformly spaced betweennine shorter rigid fingers 22. The fin gers 20, 22 are held in pocketsformed between annular sheets 74 of plastics material placed one uponthe other only one such sheet 74 being visible in FIG. 2. The fingers 20are formed with opposed pairs of substantially semi-circular depressions26 towards their radially inner ends.

The valve seat member 14 has a hollow stem 28, stepped counterbores 30,32, and 34, and passages 38 and 40, as conventionally known. Aconventional input push rod 42 locates in a socket portion 44 which isbutted against the shoulder defined between the counterbores 30 and 32.An air passage 46 communicates with passage 40 and atmosphere via afilter (not shown) which is situated coaxially of the push rod 42.

Annular valve seats 48 and 50 are located on the valve seat member 14coaxially with each other and with the head 52 of an extension 54 of theoutput rod (not shown) of the servo. A resilient valve closure member 56is located between the valve seat member 14 and the deflecting plate 18adjacent valve seats 48, 50. The closure member 56 is sealed to the head52 at 58. An annular plate 60 circumscribes the head 52 and provides ameans of distributing the weight transmitted by fingers 20, which abutthe annular plate 60. An annular support member 62 circumscribes thehead 52, abuts the ends of finger members 20 and supports a spring 64which biases the member 62, and therefore the ends of fingers 20,towards the closure member tending to maintain the closure member incontact with valve seat 50. A further annular member 66, concentric withand radially outward of the annular member 62, and U-shaped intransverse section, is provided with slots 68 through which fingers 20pass. Slots 68 help locate the fingers 20 and the channel-shaped member66 spreads reaction forces from the fingers 20 round the outer peripheryof the closure member 56. The member 62 carries a number ofcircumferentially spaced axially extending pegs 70 which locate in thedepressions 26 at the ends of fingers 20. The pegs 70 therefore catefingers in circumferential and radial directions.

An annular support member 72 is provided radially outwardly of themember 66 and circumscribes both members 66 and 62. The shortenedfingers 22 abut the support member 72 which in turn abuts the valve seatmember 14 at its outer periphery. A conventional dished fulcrum plate 74provides an annular pivot point at 76 for fingers 20, 22 of thedeflecting plate 18.

The valve seat member 14 is provided with a number of circumferentiallyspaced passages 78 which are sealed off by a flap portion 80 ofdiaphragm 12.

The arrangement shown in the drawings is in the off or vacuum suspendedstate. That is, the movable components are in their extreme right-handposition with respect to the servo body (not shown) and the valveclosure member 56 abuts the valve seat 50 thus sealing off air passage40 but is clear of valve seat 48. Thus, a state of vacuum exists on bothsides of the diaphragm 12 as the left-hand side of the diaphragm ispermanently connected to a source of vacuum (normally from the inletmanifold of the vehicles engine). This is known as the vacuum suspendedcondition.

In operation, the input push rod 42 is moved to the left, when thesocket 44 which abuts the shoulder formed between counterbores 30, 32will cause the valve seat body 14 to move to the left. The long fingers20 of the deflecting plate 18 pivot about the valve seat 50 untilclosure member 56 engages the valve seat 48, when the long fingers 20pivot about valve seat 48 thus lifting closure member 56 clear of valveseat 50. This has the effect of, firstly, sealing off the volume to theleft of the diaphragm from the volume to the right of the diaphragm whenthe valve seat 48 is contacted and, secondly, of allowing atmosphericair to reach the volume to the right of the diaphragm when the closuremember 56 is clear of valve seat 50, air travelling from atmospherethrough passages 46 and 40 rowards the valve seat 50 and thence throughpassage 38 to the volume on the right-hand side of the diaphragm 12.During this operation, the short fingers 22 pivot about their ends whichabut the annular support member 72. If the input push rod 42 is now heldin a steady position, air continues to flow through the various passagesinto the volume to the right-hand side of the diaphragm, thus pushingthe diaphragm/deflecting plate/fulcrum plate assembly slightly furtherto the left and also causing the long fingers of the deflecting plate topivot about valve seat 48 until the closure member 56 engages valve seat50 once again, when the supply of air will be shut off. In thisposition, with both valves 48 and 50 contacted by closure member 56 theair pressure to the right of the diaphragm 12 just balances the reactionforces transmitted by output rod extension 54 and the servo unit is in abalanced state. If the input force is then discontinued, the reactionthrough extension rod 54 will cause the assembly to move to the rightand the long fingers 20 will pivot about valve seat 50 thus causingclosure member 56 to lift clear of valve seat 48. In this condition bothsides of the diaphragm 12 are connected to the source of vacuum and areturn spring (not shown) biases the fulcrum plate 74 to the right untilthe servo unit is in its off state.

To provide feel for the operator of the system a certain amount of theforce developed by the servo unit should be fed back via the input pushrod 42 as a reaction force. This is achieved by ensuring that the centreof pressure (or, more correctly, the annulus of pressure) of the airpressure acting on the right-hand side of diaphragm l2 falls radiallyoutwardly of the annular pivot 76 of the fulcrum plate 74. Thus when theservo is on, the fingers 20, 22 of the deflecting plate 18 tend to pivotaround about point 76 of the fulcrum plate 74 and a reaction force isfed back via fingers 20 through the annular ring 60 and closure member56 to the valve seat body 14 and thus via socket member 44 to the inputrod 42. The short fingers 22 also pivot about the point 76 and transferreaction via the support member 72 directly to the valve seat member 14and then to push rod 42 as before.

Hysteresis effect is shown by the long fingers 20 for the followingreasons. When the input force is being applied by push rod 42 the longfingers 20 pivot about the radially outer valve seat 48, whereas whenthe input force is released and the diaphragm assembly is moving to theright, the fingers 20 pivot about the radially inner valve seat 50. Sofar as concerns the reaction force reaching the valve seat member 14 dueto the effect described in the previous paragraph, the fingers 20 may beconsidered as simple levers acting about the fulcrum 76. [f the airpressure is assumed to be constant, then the moment about the fulcrum 76is determined by the force p acting at the centre of pressure multipliedby the distance 1 between the fulcrum point 76 and the centre ofpressure. This moment pl must be balanced by the product of the reactionforce experienced by the valve seat member 14 and the distance betweenthe point of contact with valve seat member and the fulcrum 76. Now, asthe point of contact on application of the brakes is the radially outervalve seatmember 48 whereas on releasing the brakes the point of contactis the radially inner valve seat member 50, the reaction forceexperienced on applying the brakes will be greater than the reactionforce experienced on releasing the brakes because the moment am beingless, the reaction force must be greater to balance the constant momentpl. Another way of stating this is that for a given input force theoutput force will depend upon whether the servo is being applied or isbeing released, ie the hysteresis efiect described above. However, inthe arrangement provided by the invention, only three of the fingerspivot about the valve seats whereas the remaining nine fingers pivotabout support member 72 which remains at constant radius. Therefore, itwill be seen that theoretically the hysteresis effect is reduced by 75per cent. It has been found in practice that the hysteresis effect isreduced by slightly more than per cent. It has also been found, however,that a small amount of hysteresis is beneficial as it tends to preventflutter in the valve closure member.

The function of the flap 80 of the diaphragm l2, and passages 78, is asfollows. If the brakes of a vehicle are repeatedly applied with theengine switched off, the volume to the left of the diaphragm will reachair pressure as the vacuum cannot be maintained in the ab sence ofsuction from the engine. A subsequent application of the brakes wouldcause the air pressure present on the left hand side of the diaphragm toactively oppose the application of the brakes. If more pressure werethen applied via the input rod it is quite possible that the diaphragmcould be torn free of the valve seat member 14 by the pressuresinvolved. Consequently the air passages 78 together with the flapmembers 80 provide a safety valve should the air pressure on the lefthand side of the diaphragm become greater than that on the right-handside.

I claim:

1. A servo motor for a vehicle braking system of the kind including apair of fluid pressure sources of different fluid pressures, comprisingan internally hollow housing, a movable wall within said housing anddividing the hollow interior thereof into contiguous first and secondfluid chambers, a motor output member displaceable by said wall andextending externally of said housing, and fluid flow control valve meansfor selectively connecting the first chamber to said fluid pressuresources with the second chamber permanently connected to one of saidsources only, thereby enabling a fluid pressure differential to beestablished between said chambers for moving said wall within saidhousing, said control valve means comprising a valve seat member formedwith a pair of spaced passage means, a pair of relatively stationaryconcentric valve seats on said member and each circumscribing one ofsaid passage means, and a common valve closure member engageable withand selectively tiltable about each seat to thereby open the passagemeans circumscribed by the other said seat, the end of one of saidpassage means remote from said valve seats being permanently connectedto one of said fluid sources and the corresponding end of the other saidpassage means being permanently connected to said first chamber, andsaid movable wall comprising an annular elastic diaphragm whose outerperiphery is rigidly fixed relative to the housing and a deflectingplate for operating the common valve closure member, the deflectingplate comprising a plurality of first, radially extending, rigid fingersheld in circularly spaced relationship which are selectively pivotableabout each said valve seat to thereby achieve said tilting of the commonvalve closure member and a plurality of second, radially extending,rigid fingers which are shorter than said first fingers and whoseradially inner ends are located outwardly of the reaidlly outer of saidconcentric valve seats.

2. A servo motor according to claim 1 in which the first and secondfingers are supported in regularly circularly spaced relationship byretaining means.

3. A servo motor according to claim 2 in which the fingers are radiallyoutwardly divergent in shape.

4. A servo motor according to claim 3 in which the radially inner endsof said second fingers abut a first annular member located radiallyoutward of the periphery of the common valve closure member.

5. A servo motor according to claim 4 in which said first annular memberalso abuts said valve seat member for transmitting reaction forces fromsaid second fingers to said valve seat member.

6. A servo motor according to claim 5 in which the radially inner endsof said first fingers engage a second annular member locatedconcentrically radially inwardly of said first annular member andabutting said common valve closure member.

7. A servo motor according to claim 6 in which said rataining means forthe fingers comprises a plurality of pockets formed between two sheetsof plastic material,

each pocket receiving a respective one of said fingers- 8. A servo motoraccording to claim 7 in which there are three of said first fingers andnine of said second fingers.

9. A servo motor for a vehicle braking system of the kind including apair of fluid pressure sources of different fluid pressures, comprisingan internally hollow housing, a movable wall within said housing anddividing the hollow interior thereof into contiguous first and secondfluid chambers, a motor output member displaceable by said wall andextending externally of said housing, fluid flow valve means forselectively connecting the first chamber to said fluid pressure sourceswith the second chamber permanently connected to one of said sourcesonly, thereby enabling a fluid pressure differential to be establishedbetween said chambers for moving said wall within said housing, a motorinput member, and control means for controlling said valve means inresponse to actuation of :said input member, said movable wallcomprising an annular elastic diaphragm whoe outer periphery is rigidlyfixed relative to the housing and which is supported by a deflectingplate comprising a plurality of radially extending, rigid fingers heldin circularly spaced relationship by a retaining means, some of saidfingers being of different length than the remainder of said fingers.

1. A servo motor for a vehicle braking system of the kind including apair of fluid pressure sources of different fluid pressures, comprisingan internally hollow housing, a movable wall within said housing anddividing the hollow interior thereof into contiguous first and secondfluid chambers, a motor output member displaceable by said wall andextending externally of said housing, and fluid flow control valve meansfor selectively connecting the first chamber to said fluid pressuresources with the second chamber permanently connected to one of saidsources only, thereby enabling a fluid pressure differential to beestablished between said chambers for moving said wall within saidhousing, said control valve means comprising a valve seat member formedwith a pair of spaced passage means, a pair of relatively stationaryconcentric valve seats on said member and each circumscribing one ofsaid passage means, and a common valve closure member engageable withand selectively tiltable about each seat to thereby open the passagemeans circumscribed by the other said seat, the end of one of saidpassage means remote from said valve seats being permanently connectedto one of said fluid sources and the corresponding end of the other saidpassage means being permanently connected to said first chamber, andsaid movable wall comprising an annular elastic diaphragm whose outerperiphery is rigidly fixed relative to the housing and a deflectingplate for operating the common valve closure member, the deflectingplate comprising a plurality of first, radially extending, rigid fingersheld in circularly spaced relationship which are selectively pivotableabout each said valve seat to thereby achieve said tilting of the commonvalve closure member and a plurality of second, radially extending,rigid fingers which are shorter than said first fingers and whoseradially inner ends are located outwardly of the reaidlly outer of saidconcentric valve seats.
 2. A servo motor according to claim 1 in whichthe first and second fingers are supported in regularly circularlyspaced relationship by retaining means.
 3. A servo motor according toclaim 2 in which the fingers are radially outwardly divergent in shape.4. A servo motor according to claim 3 in which the radially inner endsof said second fingers abut a first annular member located radiallyoutward of the periphery of the common valve closure member.
 5. A servomotor according to claim 4 in which said first annular member also abutssaid valve seat member for transmitting reaction forces from said secondfingers to said valve seat member.
 6. A servo motor according to claim 5in which the radially inner ends of said first fingers engage a secondannular member located concentrically radially inwardly of said firstannular member and abutting said common valve closure member.
 7. A servomotor according to claim 6 in which said rataining means for the fingerscomprises a plurality of pockets formed between two sheets of plasticmaterial, each pocket receiving a respective one of said fingers.
 8. Aservo motor according to claim 7 in which there are three of said firstfingers and nine of said second fingers.
 9. A servo motor for a vehiclebraking system of the kind including a pair of fluid pressure sources ofdifferent fluid pressures, comprising an internally hollow housing, amovable wall within said housing and dividing the hollow interiorthereof into contiguous first and second fluid chambers, a motor outputmember displaceable by said wall and extending externally of saidhousing, fluid flow valve means for selectively connecting the firstchamber to said fluid pressure sources with the second chamberpermanently connected to one of said sources only, thereby enabling afluid pressure differential to be established between said chambers formovIng said wall within said housing, a motor input member, and controlmeans for controlling said valve means in response to actuation of saidinput member, said movable wall comprising an annular elastic diaphragmwhoe outer periphery is rigidly fixed relative to the housing and whichis supported by a deflecting plate comprising a plurality of radiallyextending, rigid fingers held in circularly spaced relationship by aretaining means, some of said fingers being of different length than theremainder of said fingers.